In a semiconductor manufacturing apparatus that is a substrate processing apparatus, a semiconductor wafer (hereinafter, referred to as “wafer”) that is a substrate is transferred to a processing module by a transfer unit and subjected to processing. Before the wafer is transferred to the processing module by the transfer unit, the wafer may be transferred to an alignment apparatus so that a direction and a position of a circumferential edge thereof can be detected. The transfer unit receives the wafer from the alignment apparatus to a predetermined location in the processing module to be directed in a predetermined orientation based on the detection result.
Conventionally, a wafer has a cutoff portion referred to as a notch that indicates an orientation thereof. The alignment apparatus is configured to detect the direction of the notch and the position of the circumferential edge of the wafer. However, a recent wafer having a diameter of 450 mm may have a fiducial mark (hereinafter, referred to as “alignment mark”) that is a dot-shaped laser mark, instead of the notch, near a circumferential edge of a backside thereof. Therefore, the alignment apparatus has a camera, and the alignment mark and the circumferential edge of the wafer are detected by imaging of the camera.
When the wafer has warpage, a distance between the camera and the wafer becomes different from a design value. In that case, if the camera does not have a function of automatically controlling a focus, i.e., a so-called autofocus function, the camera is not focused on the alignment mark and the circumferential edge of the wafer, which makes the obtained image blurry. As a consequence, the alignment mark cannot be detected, and the detection accuracy of the position of the circumferential edge of the wafer may deteriorate. In the case of using the camera having the autofocus function, the above problem can be avoided. However, such a camera is expensive, which increases a manufacturing cost of the alignment apparatus. Also, in the semiconductor manufacturing apparatus, it is required to accurately transfer the wafer even if it has warpage, or detect the warpage of the wafer to correct the warpage in the apparatus.
As for the alignment apparatus, there is disclosed in, e.g., Japanese Patent Application Publication No. 2009-129945, an apparatus for detecting a position of a circumferential edge of a wafer by moving a camera in a vertical direction and a diametrical direction of the wafer to follow an edge of the wafer based on a detection result of a displacement sensor. However, the configuration of the movable camera and the displacement sensor results in scaling up of the alignment apparatus. In addition, Japanese Patent Application Publication No. 2009-129944 discloses an alignment apparatus for detecting a position of a circumferential edge of a wafer by calculating an approximate equation indicating a cross sectional shape of the wafer having warpage based on a detection result of a displacement sensor. However, the alignment apparatus of Japanese Patent Application Publication No. 2009-129944 is disadvantageous in that the apparatus configuration may be scaled up due to the presence of the displacement sensor. Further, the alignment apparatus of Japanese Patent Application Publication No. 2009-129944 does not include a camera, and cannot solve the above-described problem.